/**
* extra_where
*
* Crazy function that allows extra where field to be used for user fetching/unique checking etc.
* Basically this allows users to be unique based on one other thing than the identifier which is helpful
* for sites using multiple domains on a single database.
*
* @return void
* @author Phil Sturgeon
**/
public function extra_where()
{
$where =& func_get_args();